To delete a custom field click on the check box found next to the custom field.

A warning pop up appears informing us that the values in the custom field will be destroyed. Also it informs that before you delete the custom field it should be removed from any page layouts they appear in.

Should you delete the custom field without removing it from a page’s layout, the following pop up will appear informing that the page’s layout is invalid. It has one or more destroyed custom fields. It is always advisable to remove custom fields from page layouts before deleting them.

Click on Manage page Layouts found under Page Layouts in the Admin page.

Click the Default layout of the Opportunity list.

Highlight the custom field and move it to the available data items box on the left by clicking the < arrow.

Click Save to save the changes.

The custom field is now ready for deletion. Click the check box next to the custom field and when the pop up appears click OK. The custom field is now deleted.